Cardiac Conduction System and Understanding ECG, Animation.

The cardiac conduction system explained clearly and simply.
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Please NOTE: this video talks about PQ segment, not PR interval, and this is NOT a mistake. You may have seen more of PR interval in text books, because it is used for ECG interpretation. But you should be able to find PQ segment too. These are 2 different things. The PR interval measures from the start of P wave. So PR interval = P wave + PQ segment. To understand ECG, we intentionally use PQ segment as it represents one single event, easier to understand. The PR interval is used, however, to interpret ECG. You can see how to use PR interval to interpret ECG here (this is another one of our videos): • How to Read ECG/EKG, P...
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The cardiac conduction system consists of the following components:
- The sinoatrial node, or SA node, located in the right atrium near the entrance of the superior vena cava. This is the natural pacemaker of the heart. It initiates all heartbeat and determines heart rate. Electrical impulses from the SA node spread throughout both atria and stimulate them to contract.
- The atrioventricular node, or AV node, located on the other side of the right atrium, near the AV valve. The AV node serves as electrical gateway to the ventricles. It delays the passage of electrical impulses to the ventricles. This delay is to ensure that the atria have ejected all the blood into the ventricles before the ventricles contract.
- The AV node receives signals from the SA node and passes them onto the atrioventricular bundle - AV bundle or bundle of His.
- This bundle is then divided into right and left bundle branches which conduct the impulses toward the apex of the heart. The signals are then passed onto Purkinje (pur-KIN-jee) fibers, turning upward and spreading throughout the ventricular myocardium.
Electrical activities of the heart can be recorded in the form of electrocardiogram, ECG or EKG. An ECG is a composite recording of all the action potentials produced by the nodes and the cells of the myocardium. Each wave or segment of the ECG corresponds to a certain event of the cardiac electrical cycle.
When the atria are full of blood, the SA node fires, electrical signals spread throughout the atria and cause them to depolarize. This is represented by the P wave on the ECG. Atrial contraction , or atrial systole (SIS-toe-lee) starts about 100 mili-seconds after the P wave begins.
The P-Q segment represents the time the signals travel from the SA node to the AV node.
The QRS complex marks the firing of the AV node and represents ventricular depolarization:
- Q wave corresponds to depolarization of the interventricular septum.
- R wave is produced by depolarization of the main mass of the ventricles.
- S wave represents the last phase of ventricular depolarization at the base of the heart.
- Atrial repolarization also occurs during this time but the signal is obscured by the large QRS complex.
The S-T segment reflects the plateau in the myocardial action potential. This is when the ventricles contract and pump blood.
The T wave represents ventricular repolarization immediately before ventricular relaxation, or ventricular diastole (dy-ASS-toe-lee).
The cycle repeats itself with every heartbeat.
All images/videos by Alila Medical Media are for information purposes ONLY and are NOT intended to replace professional medical advice, diagnosis or treatment. Always seek the advice of a qualified healthcare provider with any questions you may have regarding a medical condition.

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[@zaynumar0]

Not digging Medicine , just watching this for fun

[@leburbuprieta]

thank you from my apex

[@jessicawagner4556]

Finally found a video that nicely connects ECGs with the pumping of the heart. Thanks

[@usergroupX]

thank you from the bottom of my ... heart i guess

[@MrHei913]

Sometimes I wonder why am i paying so much for my school fees when i dont get high quality lecture like this one over here hahaha

[@SofiaL1D]

this is pure gold for studying for my physiology class! amazing

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[@DaleHerringTV]

Thank you so much. I've acquired bits and pieces throughout the unit, but haven't had a clear picture. This brought all of the pieces of the puzzle together. Thorough and informative, yet short and condensed; Just how I like it. Thanks again!

[@Alilamedicalmedia]

Please NOTE: As we got this question a lot, we just want to clarify here: This video talks about PQ segment, not PR interval, and this is NOT a mistake. You may have seen more of PR interval in text books, because it is used for ECG interpretation. But you should be able to find PQ segment too. These are 2 different things. The PR interval measures from the start of P wave. So PR interval = P wave + PQ segment. To understand ECG, we intentionally use PQ segment as it represents one single event, easier to understand. The PR interval is used, however, to interpret ECG. You can see how to use PR interval to interpret ECG here (this is another one of our videos):

[@MoveInSilence2444]

This is the absolute best description of what is going on in the heart during the EKG on the INTERNET! THANK YOU!

[@yasmine9046]

This is so well explained I want to cry! You are doing an amazing job showing us that there are no difficult chapters, only poorly explained ones.

[@tby62]

My 3yo has a resting heart rate of 53 from 68 when she was 2yo... she likely has progressed to 3rd degree heart block... this video has helped me to visualize and understand the function of the heart. Thank you

[@Liz-pl1bx]

I'm 16 and these videos help me to study biology on purpose to pass school exam. The way of explanation and colorful pics are fabulous! Thank you very much, greeting from Russia 😁👋

[@dentfortune7271]

It’s amazing how the ECG shows how action potential is moving across the membrane. From SA node to AV node action potential is facing (+) ^ PR interval. From AV to left Bundle Brunch( -) PR segment and negative deflection QRS complex( ventricular depolar/ atrial repolar. When the base is being depolarized (^ +), the signal continues upwards(-) etc.

[@TheSMCSS1234]

wow, this video basically explains whole chapter about Cardiac physiology. I did not understand cardiac events in the class, but i understood here. I just have to study the notes i took while listening to your video. I appreciate you had subtitles too which made a lot easier. Very useful

[@ShesArizza]

thank you this was so easy to follow especially having the heart animation shown as the waves go by to show how the heart pumps blood throughout. very easy to understand than my prof's notes!

[@saisubhash1615]

Wow. Why can't everybody explain like you. Hatsoff sir. Thank you for this video.

[@kimsordyl]

I absolutely love this concise yet detailed explanation! Thank you

[@randomfyasmry]

This is why I appreciate KZbin. I finally understand this in under 4 minutes rather than a lecture for 5 hours and reading the textbook that has too many pages that explains this